Process of manufacturing pure nitric oxid.



UNiiiED STATES PATENT OFFICE.

RUDOLF M'U'LLEIQ. VON BEBNECK, MARTIN MOEST, AND HUGO GRAD, OF HfiUHST-ON- THE-MAIN, GERMANY, ASSJlG-NORS T0 FARZBW ERKE VORM. MEISTER LUCIUS &

BRYU'NING, 0F H6CHST-ON-THE-MAIN, GERMANY, A CORPORATION OF GERMANY.

PnocEss or manuracrumno roan man-1c oxm.

1,021,234, Specification of Letters Patent. No Drawing. it Application filed May 10, 1911.

To all whom itmag concern Be it known that we, RUnoLr MtiLLER VON BERNECK and MAR'rIN Mons'r, Ph. D., and HUGO GRAF, Ph. 'D., citizens of the Empire of Germany, residing at Htichst-on-the- Main, Germany, have invented certain new and useful Improvements in the Process of Manufacturing Pure Nitric Oxid, of which -the following is a specification.

It is known that by the electrolysis of nitric acidin the cathode compartment of an electrolytic cell various products can be obtained. By using diluted nitric acid at a moderate temperature there are produced substantially ammonia and at the same time some other products of reduction of the nitric acid, among them even elementary nitrogen. According tothe process described in U. S. Patent No. 887 ,266, when nitric acid is heated and subjected to the action of the electric current, it evolves at the cathode the easily-condensable nitrogen dioxid, or a mixture of nitrogen dioxid and nitric oxid. However, all endeavors to modify the rocess so as to obtain pure nitric oxid NO) have been hitherto unsuccessful. We have now made the surprising observation that when the nitric acid to be subjected to electrolysis at the cathode contains nitrous acid, a nearly chemically pure nitric oxid (99-100 per cent. strength) is obtained in almost quantitative yield. In the following specification there are always implied by nitrous acid also the nitric oxids N 0 and NO (N,O,,), which form in presence of water nitrous acid.

The formation of the nitric oxid is substantially due to the reduction of the nitric acid, while the nitrous acid present is attacked only to a very small extent, so that there is possibly a catalytic action of the nitrous acid. As electrodes may be used carbon or graphite,.or the metals capable of resisting attack by nitric acid, such as gold or platinum. Among these materials carbon or graphite, and platinum or its alloys, have proved to be most suitable. These electrodes require a comparatively weak tension and furnish entirely pure'nitric oxid, whereas, when using certain other electrodes,

Patented Mar. 26, 1912. Serial no. 628,191.

for instance aluminium electrodes, some other products of reduction of the nitric acid are produced causing losses of nitrogen. wise similar conditions, a considerably higher tension at the electrodes when aluminium cathodes are used.

The concentration of the nitric acid used may vary within wide limits; however it is advantageous not to exceed a percentage of 40, because otherwise nitrogen dioxid is formed in addition to nitric oxid, especially at a raised temperature. The percentage of nitrous acid contained in the nitric acid may also be considerably varied, but even 1% or less suflices to give favorable results. Itis remarkable that the minimum amount of nitrous acid, in order to obtain a pure nitric oxid, depends on the material used for the electrode, the conditions of the electric current and the concentration of the nitric acid. For instance when nitric acid of 20-30 per cent. strength and a currentdensity of 5-10 amperes per square decimeter are used at ordinary temperature, the said minimum amount of nitrous acid is: for cathodes made of carbon (graphite) below 1% of HNO for cathodes made of platinum-foih'abOut 1.2% of HNO. forv cathodes made of gold-platinum alloy, about 1.9% of HNO It is advisable to keep the temperature moderate.

The anode compartment is preferably charged for instance with nitric acid containing nitrous acid, in which case the anodic oxygen is used in oxidizing the nitrous acid, with formation of nitric acid. Of course, there may also be used other suitable electrolytes in the anode compartment, for instance sulfuric acid or nitric acid.

The present process has the advantage that the nitric oxid, which has not been obtainable hitherto by electrolysis ina pure form, can be produced in a very cheap way and pure state while avoiding losses of nitrogen. The nitric oxid thus obtained can be easily dried, for instance by means of concentrated sulfuric acid. By adding a corresponding quantity of pure dry oxygen or a suitable dry mixture of gases contain- There is also require under other-' ing oxygen, for instance air, it is possible acid to electrolysis at a cathode capable of to prepare nitrogen dioxid absolutel free resisting attack by nitric acid. from nitric acid and easily condensab e. In In testimony whereof, we aflix our signathis ure liquid formit is fit for transport tures in presence of two witnesses.

'5 and or being made up into other products. RUDOLF MULLER VON BEBREQK. Having now described our invention what 7 MARTIN MOEST. we claim is: HUGQ GRAF. ;'-"TheNprocess of pre aring pure nitric Witnesses: oxid O) by electrolysls, which consis ts in JEAN GRUND,

1'0 subjecting nitric acid containing nitrous CARL GRUND. 

